1. Field of the Invention
The present invention relates generally to photographic cassettes, and particularly to a device and method usable with such cassettes for facilitating removal of a photographic sheet therefrom.
2. Description of the Prior Art
U.S. Pat. Nos. 3,784,835 and 4,198,009 describe x-ray film sheet cassettes of a type suitable for daylight loading and unloading in cooperation with film supplying and film processing apparatus. Such cassettes typically have a rectangular-solid configuration defined by six orthogonally joined walls which enclose a chamber for accommodating an x-ray film sheet. In one of those walls is a light-shielded slot through which a film sheet can pass into and out of the chamber. Within the chamber, in alignment with the slot, is a pair of opposing planar surfaces relatively movable toward and away from each other to prevent and permit, respectively, movement of a film sheet therebetween. One of those surfaces is spring-loaded toward the other to clamp a film sheet flat between them. Means are provided for urging the two surfaces apart in response to placing the cassette into operative relationship with suitably configured film supplying or film processing apparatus, thereby allowing a film sheet to slide between those surfaces when the cassette is positioned for loading or unloading. When so positioned, the cassette is intended to be loaded or unloaded by the simple expedient of letting a film sheet drop into or out of the chamber by force of gravity.
It has been found that gravity alone does not always suffice to effect desired unloading when such a cassette is appropriately positioned with its slot facing downward and its planar surfaces spread apart. This is believed due primarily to a lack of air between the sheet and one of those surfaces, resulting in a state of contact between the sheet and the one surface which may best be described as "pseudo-optical" in both nature and effect. The effect in this case has been a tendency of the sheet to cling to that one surface, rather than simply fall away from it.
There has thus existed a need for an efficient and reliable way to prevent or overcome that tendency. Efforts to meet this need by roughening the planar surfaces have not proven entirely successful. Attempts at nudging the sheet directly toward the cassette slot likewise have not succeeded in overcoming the clinging effect. This need has remained unresolved by all such past endeavors.